I have a 93 F150 with a 5.0 that idles rough and at times will start to miss when going up hills, especially if the engine is not up to temp. I have changed the fuel filter and plugs wires and cap and rotor. I have also cleaned the idle valve and set the timing to 10 degrees BTDC with the spout off. The miss will come and go at idle and the high speed miss goes away by itself as if the computor corrects what ever is causing the miss. Any help would be greatly appreciated.

 

You cleaned the IAB??This is the idle air bypass. It is attached to the throttle body. If you removed it and cleaned out the two holes, then that should be OK. Did you clean the throttle body? They get gummed up too. Open the throttle valve and wipe it out with a rag and carb cleaner. Does it do this when just started up? Or does it take a few minutes to begin to miss?? This would help as it determines whether it is happening during open loop or closed loop. Have you ever replaced the O2 sensors?? Theya re the only part that will degrade as you use the vehicle. They should be replaced after about 50K. You will usually see better fuel mileage and improved engine response. Is the idle spped good?? You did change the fuel filter right? I know you did the plugs and wires.

 

Thanks for the reply> I know I misses a few items in my post regarding what I have already done so here goes... the first thing I did was change the fuel filter and plugs then the cap and rotor and then new wires when it ran real bad one day on my way to work very rough with a sharp metalic snapping sound not like ping at all. Still no change in idle or running. I have cleaned the IAC and throttle body too This corrected my idle stall when the a/c and power steering were used at the same time.I have cleaned and checked the EGR as well as the vaccuum valve that controlls it. This item was really dirty and there was a small change in performance after this was done. I have even made a Stainless steel shimstock plate to block off the EGR to the manifold to eliminate exhaust gasses to the intake, mild improvement so it is still in there. After reading my Haynes manual over and over I decided to check the timing. It read 5 degrees BTDC with the spout disconnected so I advanced it to 10 and reconnected the spout. It still idles rough (cold and warm) but now the miss on up hill runs only happen when it is not up to operating temp. I haven't been able to detect any vaccuum leaks as yet ( I do need a guage tho) but I understand that these motors are subject to intake gasket failure between top and bottom halves. Odd that this gasket could fail soI suppose I will have to relace it as my next course of action (cheap part, time consuming job) There is also no difference in type of gas i use or which tank I am on. I have also done a running test on the fuel rail pressure and it is 38psi at idle. when I disconnect the vaccuum line to the reg. it goes up over 40psi. The only eng lite I have had was regarding the EGR not opening and this was due to the solinoid being so dirty, there was a piece of dirt holding the little valve disk partly open and the filter on top was plugged. The miss I have is like a plug is not firing all the time but it comes and goes. Perhaps it is a dirty injector. I unfortunatly do not have dual exhaust so I cannot isolate which side of the engine is missing which would be a great help. The truck is a high (27000km) miler but does not burn oil and is getting 18-20mpg (imperial) at the moment which I gather is damn good for a 4x4 clubcab 5spd long box with 31/10/15 tires. I hope this info will be of some help.

 

I am having a similar problem with my 351w. My uncle teaches in Missouri at a Ford Tech school and he told me to check a few things. First off, you shouldn't have the EGR tube blocked off. That can cause some back firing and some pinging. Did you check the O2 sensor? You have already cleaned the throttle body etc. so I wont mention any of that. The injectors could be plugged up, try cleaning them. Try running some premium gas (if you dont already). Hope this helps